Process for production of saline-solution soluble xanthan gum

ABSTRACT

A process for saline-solution soluble xanthan gum which comprises the steps of precipitating xanthan gum by mixing, with stirring, an aqueous solution of xanthan gum with an organic solvent which is a non-solvent to xanthan gum but is hydrophilic, removing liquid from the precipitated xanthan gum to a liquid content of at most 50%, disintegrating the cake of xanthan gum after the liquid removal to an average grain size of from 0.3 to 2 cm in diameter, and drying the disintegrated xanthan gum by fluidizing the same at a temperature not exceeding 80° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

The priority of prior copending provisional application Ser. No.60/000,870, filed Jul. 11, 1995, is claimed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The priority of prior copending provisional application Ser. No.60/000,870, filed Jul. 11, 1995, is claimed.

BACKGROUND OF THE INVENTION

The present invention relates to a process for modifying xanthan gum toobtain a xanthan gum having enhanced solubility in saline solution.

Xanthan gum is a naturally occurring high molecular weightpolysaccharide and has found a wide scope of uses, particularly as athickener or viscosity modifier for aqueous based compositions. Forexample, it has found extensive use in the food, cosmetic and oilindustries. The ability of xanthan gum to effectively modify an aqueoussolution is directly related to its solubility in the aqueous medium.Since in such uses, the aqueous compositions generally contain sodiumchloride or other salts, it is desired that the xanthan gum have as higha solubility in such salt solutions as possible. However, xanthan gumwhich is conventionally obtained from the fermentation of Xanthomonascampestris does not exhibit a particularly high solubility in salinesolution, and in particular, saline solutions having relatively highsalt concentrations.

A process for obtaining a modified xanthan gum which exhibits enhancedsolubility in aqueous solutions of salts, such as, sodium chloride, isdisclosed in U.S. Pat. No. 5,416,206. As described therein, and asreferred to herein, enhanced solubility means that the xanthan gumexhibits a viscosity of not less than 800 mPa as determined on a 0.5% byweight solution thereof in a 12% by weight aqueous sodium chloridesolution at 20° C. at 30 rpm using a Brookfield BL viscometer and havinga ratio of this viscosity to that determined on a 0.5% by weightsolution thereof in distilled water of not less than 1.5.

This process requires equipment for forming fine fibers of theprecipitate while mixing an aqueous solution of xanthan gum with anorganic solvent which is a non-solvent to xanthan gum but ishydrophilic. Japanese Patent Provisional Publication Nos. Sho58-5301(5301/1983) and Hei 1-318001(318001/1989) teach a method fordrying xanthan gum directly as precipitated in the form of lumps ratherthan fine fibers. The dried lumps, despite subsequent grinding, giveproducts sometimes with unfavorably affected properties, such as, lowsolubility in aqueous saline solutions and other salts. In view of this,there has been need for a way of obtaining xanthan gum of good qualityeven through the conventional precipitation process.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aprocess for preparing xanthan gum having improved solubility in salinesolution. Another object is to produce the saline soluble xanthan gumwith decreased energy costs.

The above object of the present invention can be accomplished byproviding a process for saline-solution soluble xanthan gum whichcomprises the steps of precipitating xanthan gum by mixing, withstirring, an aqueous solution of xanthan gum with an organic solventwhich is a non-solvent to xanthan gum but is hydrophilic, removingliquid from the precipitated xanthan gum to produce a xanthan gum cakehaving a liquid content of at most 50%, disintegrating the cake ofxanthan gum after the liquid removal into particles having an averagesize of from 0.3 to 2 cm, and preferably, from about 0.6 to 1.5 cm indiameter, and drying the particles of xanthan gum at a temperature notexceeding 80° C.

According to the present invention, the cake of precipitated xanthan gumis broken into particles by conventional means so that speciallydesigned equipment is not required. The drying can be concluded within ashort time period while the xanthan gum is maintained substantially inthe particulate state, whereby a xanthan gum exhibiting excellentsolubility in saline is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention and wherein:

FIG. 1 is a schematic view illustrating a stirred tank for use in thepresent invention;

FIG. 2 is a sectional view illustrating essential parts of a V-type diskpress for use in the invention;

FIG. 3 is a sectional view taken along line II--II in FIG. 2;

FIG. 4 is a front view of either screen 2a or 2b;

FIG. 5 is a sectional view taken along line III--III in FIG. 4;

FIG. 6 is a sectional view of a disintegrator for use in the invention;and

FIG. 7 is a side view of a dryer for use in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fermentation Step

The present invention in its practice may use an aqueous solution ofxanthan gum, e.g., a fermentation broth containing dissolved xanthan gumas produced by the fermentation of, for example, Xanthomonas campestris,and a solution obtained by dissolving xanthan gum which has beenpreviously precipitated and separated and/or processed, e.g., subjectedto clarification treatments, and the like, in an aqueous solution.

Xanthan gum is prepared by well-known fermentation processes. Forinstance, it is produced by placing a bacterium belonging to the genusXanthomonas, i.e., X. campestris, under appropriate fermentationconditions. (This compound and the process for producing the same aredescribed in U.S. Pat. No. 3,659,026, the contents of which areincorporated herein by reference.)

In producing xanthan gum, Xanthomonas campestris as a xanthangum-producing microorganism may be replaced by any other knownXanthomonas species. Examples are X carotate, X incanae, X begoniae, Xpapavericola, X translucens, X vasculorum, and X hederae.

Precipitation Step

The xanthan gum to which the present invention applies is preparedconventionally by preliminary fermentation and main fermentation of axanthan gum-producing bacterium on a suitable culture medium. It isusually obtained as a xanthan gum fermentation broth.

In the practice of the invention, the fermented solution is sterilized(heat treated), and the resulting aqueous xanthan gum solution is mixedwith an organic solvent which is a non-solvent to xanthan gum but ishydrophilic by feeding them together to a tank equipped with agitatingblades capable of high-speed agitation and mixing. The agitation-mixingin the tank causes precipitation of xanthan gum.

For the efficient mixing of a highly viscous aqueous xanthan gum and ahydrophilic organic solvent and also for the satisfactory recovery ofthe precipitated xanthan gum, the use of an agitation system thatinvolves high-speed reciprocating motion of the blades is recommended.Ordinary agitation using one-way revolution allows precipitating xanthangum to stick to the blades and often the precipitate is difficult torecover. The blade diameter/tank diameter ratio is desirably 0.5 ormore. If the ratio is less than 0.5, stagnant regions develop along theinner walls of the tank, where the aqueous solution of xanthan gum andthe hydrophilic organic solvent become immiscible.

The xanthan gum to be handled under the present invention is notspecially limited. The invention can be used for any fermented solutionsor broths of xanthan gum with or without subsequent filtration ortreatment with chemicals or the like, and aqueous solutions in whichpreviously recovered xanthan gum has been redissolved. Also, thecomposition of the aqueous solution, as well as its xanthan gumconcentration, ph, temperature, and concentrations of other additivesare not limited.

The hydrophilic organic solvent incapable of dissolving xanthan gum thatis used in precipitating xanthan gum may be an alcohol such as methanol,ethanol or isopropanol, or dioxane, acetone, tetrahydrofuran or thelike.

Liquid Removal Step

The xanthan gum precipitated by the process, at this stage contains atleast about 80% by weight liquid. Drying the precipitate in this stateadds substantially to the energy cost and requires high temperature andmuch time. Moreover, it is prone to overdrying, which undesirablyaffects the solubility of the xanthan gum in saline solutions. To avoidthese, it is important to remove liquid from the xanthan gum to reduceits liquid content to 50% or less.

In the liquid removal step where the present invention is embodied, adispersion containing precipitated xanthan gum is fed to a V-type diskpress having a pair of revolving disk-shaped screens, the space betweenwhich decreases as the screens revolve. The xanthan gum dispersion isthus squeezed by the pair of disk-shaped screens, and its liquid contentpressed out through the screens and recovered, while the xanthan gum iscompressed into a cake which revolves with the screens until it isdischarged for recovery.

Disintegration Step

The xanthan gum cake after the liquid removal takes the form of smalllumps or long cords. This precipitate can retain interior regions ofhigh-liquid-content regions. To completely dry the xanthan gum in thisform would require elevated temperatures and long drying times, which,in turn, adversely affects the saline-solution solubility of theproduct. In accordance with the present invention, the xanthan gum cakeobtained is broken or disintegrated into small grains or particles,which allows for the drying to be carried out at a sufficiently lowtemperature so as not to adversely affect the saline solubility of theproduct.

The disintegration method is not specially limited, but in the practiceof the invention the use of a cutter provided with a screen isdesirable. The average grain diameter of the xanthan gum thus broken outis preferably between 0.3 and 2 cm, and more preferably between 0.6 and1.5 cm. A diameter larger than 2 cm is not recommended because itnecessitates a high temperature treatment to dry up the interior of thexanthan gum grains. On the other hand, breaking down the cake into finerpieces of less than 0.3 cm in diameter is also undesirable since it cancause screen clogging or other problems which lead to reducedproductivity.

Drying Step

The xanthan gum disintegrated by the afore-described method is dried ata temperature not higher than 80° C. The drying method is not speciallyrestricted but a system of the type that fluidizes the xanthan gumgrains during the process of drying is desirable. The drying temperatureshould not exceed 80° C. Otherwise, the saline- solution solubility ofthe product will be undesirably decreased.

Grinding Step

In practicing the invention, it is possible to grind the dried xanthangum to a sufficiently fine size to facilitate the dispersion in salinesolutions. The grinding method may be any of the methods in common use,e.g., impact grinding.

The invention will now be described in more detail with reference to theaccompanying drawings showing a preferred embodiment thereof.

FIG. 1 illustrates a preferred form of tank for use in the precipitationstep according to this invention. In FIG. 1, numeral 101 indicatesdrives including a motor for driving an agitator shaft, 102 indicates astirred tank, and 103 indicates the agitator shaft 103. Agitator shaft103 is provided with upper and lower agitating blades 104 and 105,which, in opposing pairs, extend from agitator shaft 103 in the left andright directions as viewed in this figure. In the embodiment beingdescribed, each pair of agitating blades 104 or 105 has longitudinalaxes on the same plane. Agitating blades 104 and 105 are triangular incross section and are each tapered.

The number and cross sectional contour of agitating blades 104 and 105are not limited to those embodied here but any other number and/orcontour may be adopted unless it departs from the purposes of theinvention.

Agitating blades 104 and 105 are capable of stirring and mixing at highspeeds, turning back and forth at every quarter of a revolution.Ordinary agitation that involves one-way blade revolution often causesthe precipitated xanthan gum to stick so fast to the blades that it canhardly be recovered. The above-mentioned reciprocating motion can beproduced by a known mechanism for the transmission of rotation from thedrive motor to the agitator shaft 103. It is, of course, possible tocontrol the drives with the provision of microprocessor-based controlsso as to effect such reciprocating motion.

The blade diameter/tank diameter ratio is desirably 0.5 or upwards. Aratio of less than 0.5 is undesirable because it forms a stagnant regionclose to the inner wall of tank 102, where an aqueous solution ofxanthan gum and a hydrophilic organic solvent cannot be mixed. The tankis supplied with an organic solvent (isopropanol) which is a non-solventto xanthan gum but is hydrophilic and an aqueous solution of xanthangum. Mixing them with stirring in the tank permits the precipitation ofxanthan gum. After the precipitation procedure, a dispersion containingthe precipitated xanthan gum is fed to a V-type disk press shown inFIGS. 2 and 3.

FIGS. 2 and 3 illustrate a preferred form of the V-type disk press foruse in the liquid removal step (referred to herein as a "V-type diskpress"). In these figures, reference numeral 1 indicates the main bodyof the V-type disk press, 2a and 2b are screens, 3a and 3b are spindles,4a and 4b are supporting arms, and 5 is a hydraulic cylinder (orspring-loaded cylinder).

The pair of screens 2a and 2b, as can be seen, are disk-shaped (orconical) and fixed to rotating supports 11a and 11b. The space betweenscreens 2a and 2b is the widest on the raw material inlet side A and thenarrowest on the opposite side B that is 180 degrees apart. Screens 2aand 2b are divided into 6 segments each when viewed from the front as inFIG. 4. Each segment consists of a punched metal plate 20 in which alarge number of small openings 21 are made evenly throughout. Itsrelative open area is governed by the size (of the screen mesh) andnumber of the small openings 21. The punched metal plate 20 is suitablystrengthened on the rear side by a reinforcing plate 22 to withstand thepressures during pressing (FIG. 5). The reinforcing plate 22 has larger,uniformly spaced openings 23.

In this embodiment, the size of the individual small openings (of thescreen mesh) is desirably not greater than 1 mm², and screens havingcircular or slit-like openings are used. Meshes greater than 1 mm² arenot desired because of large loss of xanthan gum through the screensupon pressing. As FIG. 3 shows, the spindles 3a and 3b are disposed in apair, on the left and right, fixedly supported by supporting arms 4a and4b, respectively, and connected rockably relative to each other by acenter pin 6 at the center of main body 1. Center pin 6 is fixed at bothends to main body 1. Supporting arms 4a and 4b are L-shaped and fixedlysupport spindles 3a and 3b at one end in the manner described above andare connected to each other at the other end through hydraulic cylinder5 or a spring-loaded cylinder. In the neighborhood of hydraulic cylinder5, supporting arms 4a and 4b are displaceably connected to the main bodywith links 7a and 7b, respectively. Numeral 8 designates a pivot forlink 7a and supporting arm 4a, and 9 designates a pivot for links 7a and7b. Of course, this mechanism includes a pivot for link 7b andsupporting arm 4b but it cannot be seen in FIG. 3. Pivot 9 can slide upand down within a recess 10 (thus constituting a slider).

A combination of main body 1, center pin 6, supporting arm 4a integralwith spindle 3a, pivot 8, link 7a, pivot 9, and recess 10 formsrevolving slider crank mechanism. Similarly, main body 1, center pin 6,supporting arm 4b integral with spindle 3b, pivot 8, link 7b, pivot 9,and recess 10 combinedly form a revolving slider crank mechanism. Owingto these mechanisms, it is made possible, by regulating the openingangle of links 7a and 7b through the lateral movement of hydrauliccylinder 5 or spring-loaded cylinder, to adjust the angle betweenspindles 3a and 3b cooperating with those elements and thereby controlthe degree of opening of screens 2a and 2b and hence the pressing force.

While revolving slider cranks are used in this embodiment as mechanismsfor regulating the degree of opening of the screens, any other mechanismcapable of regulating the spindle angle may be employed instead underthe invention, such as quadric crank chains in which the sliders arereplaced by links.

As shown in FIG. 3, rotating supports 11a and 11b are rotatablysupported by spindles 3a and 3b, respectively, via bearings and arerotated by driving forces transmitted to sprockets 12a and 12b integralwith the supports (through endless chains). Alternatively, any ofvarious other mechanisms, e.g., V-belt transmission, may be used forpower transmission to rotating supports 11a and 11b.

The material fed to the raw material inlet A is held between screens 2aand 2b and is gradually squeezed as screens 2a and 2b revolve, with itswater content flowing out through the screens to their back side. Thefeed is subjected to maximum compression at point B, 180 degrees apartfrom the inlet, and then the spacing between screens 2a and 2b increasesgradually, and a dewatered cake is discharged along a scraper 2013. Inthis way, a xanthan gum component in the form of a cake can berecovered.

The rate at which a dispersion of xanthan gum is fed to the V-type diskpress is suitably chosen in consideration of the factors including thexanthan gum concentration in the dispersion and the state ofprecipitation of xanthan gum.

Unlike centrifugal separators that utilize the difference in specificgravity, the V-type disk press of this embodiment depends oncompression. The degree of liquid removal can be adjusted with thecompression pressure and the speed of screen revolution, whereby thexanthan gum is squeezed to a water content of only 40-50% by weight.Consequently, the cleaning and purifying effect of the hydrophilicorganic solvent is improved and the energy load on the ensuing dryingstep is lessened.

The V-type disk press shown in FIGS. 2 and 3 can squeeze the feed at lowspeeds of screen revolution, usually in the range of about 1 to 12 rpm(for screens 0.5 to 1.5 m across). Compared with centrifugal separatorsthat run at 500 to 2,000 rpm, it requires far less power for itsoperation. Another advantage is the higher degree of safety becausethere is no need of running the press at high speed in the presence ofan organic solvent.

After the liquid removal step, the cake of xanthan gum is transferred toa disintegrator as shown in FIG. 6, where it is broken up into xanthangum grains from 0.3 to 2 cm in diameter.

FIG. 6 illustrates a preferred form of the disintegrator.

In FIG. 6, 601 is the main body of the disintegrator, 602 is a hopper,603 is a treating tank, 604 is a rotary cutter, and 605 is a screen.

Treating tank 603 is built as a cylinder, in which rotary cutter 604runs. Rotary cutter 604 has three revolving cutter blades 606. The cakeof xanthan gum fed at the hopper 602 is broken up into pieces by thecutting blades 606 of rotary cutter 604 in treating tank 603. The piecesdisintegrated to a given size or finer are discharged through screen 605and then through an outlet 607. The size of the resulting xanthan gumgrains can be controlled through the adjustment of the mesh size ofscreen 605. While the embodiment shown uses three revolving cuttingblades, the number of blades is not a limitation to this invention. Thedisintegrated xanthan gum is then sent to a dryer as shown in FIG. 7 fordrying.

FIG. 7 illustrates a preferred form of the dryer. This dryer 701 is of atype which fluidizes xanthan gum grains during the process of drying,and is set to a drying temperature not exceeding 80° C. Dryer 701includes a drying drum 702 which is rotated as a rotating shaft 703 isdriven. Rotating shaft 703, shown at right, is driven with rotationalforces transmitted from a drive motor 704. 705 is an inlet and 706 is anoutlet. Hot water enters the dryer 701 from a pipe 707b on the right andflows through a pipe 711b into jackets 710 so as to adjust thetemperature of dryer 701. After circulating through jackets 710, the hotwater flows out through a pipe 711a and finally through a pipe 707a. Thetemperature inside the dryer 701 can be regulated by setting the hotwater temperature to a desired level.

Vapor-laden air is released under reduced pressure from a vent pipe 708at the left end. This construction is realized by using a hollowrotating shaft 709 on the left and adopting other means known in theart. The dried xanthan gum is discharged from outlet 706, and it may beground for easier dispersion in a saline solution. Impact grinding ispreferred for that purpose.

Along with the embodiment thus far described, the process of theinvention was tested. The results were as follows.

TESTING EXAMPLE 1

A liquid culture medium of the composition I given below was placed in a2,000-liter fermenter, inoculated with a culture of Xanthomonascampestris that had resulted from 24-hour preliminary cultivation, andincubated under aeration and agitation for 2 days, when a fermentedsolution containing 30 g/e of xanthan gum was obtained.

    ______________________________________    Culture medium composition I    ______________________________________    Glucose        58            g/l    Polypeptone    2             g/l    KH.sub.2 PO.sub.4                   2             g/l    MgSO.sub.4.7H.sub.2 O                   0.5           g/l    Water          1,300         l    ______________________________________

The fermented solution was heated at 70° C. for 30 minutes to kill thexanthan gum-producing bacteria, and 480 of the xanthan gum fermentedsolution and 720 of aqueous isopropanol (water content: 15 wt%) werepoured into a 1,600-liter precipitation tank of the constructiondescribed above in conjunction with FIG. 1. The charge was mixed withstirring by an agitation blade (the blade diameter/inside diameter ofthe tank: 0.86, triangular blade, "Adzita AG type" manufactured byShimazaki Seisakusho K.K.) that turns reversely after running eachquarter of a revolution at high speed within the tank, and xanthan gumwas precipitated. The precipitated xanthan gum was in the form of a longcord about 30 to 40 cm in length having a diameter of from about 2 to 3cm..

The dispersion containing the xanthan gum was fed at a rate of 1,500liters per hour to a V-type disk press of the construction alreadydescribed with reference to FIGS. 2 and 3 ("Asahi Press C-35," mfd. byAsahi Koki K.K., screen mesh size: 0.5 mm) for liquid removal. Theliquid content in the product after primary liquid removal was 60% byweight. To 30 kg of the product after primary liquid removal was addedone equivalent weight of isopropanol (water content: 15%) in a 500-literstirred tank. After stirring, the resulting dispersion was fed again tothe V-type disk press under the same conditions as described above forliquid removal. The xanthan gum product as a cake after the secondaryliquid removal had a liquid content of 45% by weight.

The cake after the secondary liquid removal was broken into small piecesusing a disintegrator of the construction explained above in conjunctionwith FIG. 6. The disintegrated xanthan gum was in the form of grainsfrom 0.6 to 1.5 cm in diameter.

In a 100-liter conical vacuum dryer of the construction illustrated inFIG. 7, 15 kg of the xanthan gum grains was dried at a dryingtemperature of 40 to 65° C. and a drying pressure of 40 to 100 torr for3.5 hours. The dry matter was ground to obtain a saline solution-solublexanthan gum finely divided to 80 mesh or finer particles.

One gram of the xanthan gum thus obtained was placed in a 500 m-tallbeaker, and it was moistened by adding 3 g of 99% ethanol. Next, 196 gof an aqueous solution of 12 wt% sodium chloride kept at 20° C. wasadded, and the mixture was stirred using an anchor agitator at 1,000 rpmfor 2 hours. Thorough dissolution of the xanthan gum and an increase inthe viscosity of the aqueous sodium chloride solution were confirmed.

The resulting solution was allowed to stand at 20° C. for one hour, andthen its viscosity was measured with a Brookfield BL type viscometer.The viscometer speed was set to 30 rpm and the viscosity was measuredwith spindle No. 2, when the viscosity (1) was found to be 900 mPa.s.Then, the xanthan gum was dissolved in distilled water to form asolution at a concentration of 0.5 wt%. Its viscosity was measured usinga Brookfield BL type viscometer at a speed of 30 rpm, with spindle No.2. The viscosity (2) was 500 mPa.s.

It was found that, in dissolving the xanthan gum in a saline solution,an agitation speed of 800 rpm or more gives good result. Theconfiguration of the agitation blade is not specially limited; any shapeis desirable if it permits the blade to fluidize the entire solution.Dissolution under these conditions produces a solution, which attains astable viscosity after about 60 minutes of agitation. It was also foundthat further agitation for 2 to 12 hours causes little change in theviscosity.

Comparative Example 1

One kilogram of xanthan gum grains obtained in the same manner asdescribed in Example 1 was dried in an air-blast dryer above 85° C. for3.5 hours. It was then ground to an 80 mesh or finer xanthan gum powder.This finely divided xanthan gum was subjected to viscosity measurementby the same method as used in Example 1. The viscosity in salinesolution, referred to as (1), was 350 mPa.s, the viscosity in distilledwater (none-saline), referred to as (2), was 500 mPa.s, and (1)/(2) was0.70. In the saline solution, many particles remained undissolved evenafter 2 hours of agitation. Continued agitation up to 12 hours stillfailed to dissolve the undissolved particles.

Comparative Examples 2 and 3

The cake of xanthan gum obtained by liquid removal in the mannerdescribed in Example 1 was disintegrated using screens with mesh sizesof 2 or 3 cm. Generally in conformity with the procedure of Example 1,the disintegration products were dried until their water contentsdropped to 10% or less. Grinding after the drying produced fine xanthangum powders of 80 mesh or more. These xanthan gum products weresubjected to viscosity measurements as in Example 1. The results areshown below.

                                      TABLE 1    __________________________________________________________________________          Mesh             Av. Part.                  Drying                      Drying                            Drying                                 Viscosity          Size             Dia. Time                      Pressure                            Temp.                                 (1)  (1)/(2)    __________________________________________________________________________    Comp. Ex. 2          2 cm             1˜2 cm                   5 hrs                      40˜100 torr.                            40˜80° C.                                 800 mPa·s                                      1.6    Comp. Ex. 3          3 cm             2˜3 cm                  10 hrs                      40˜100 torr.                            40˜80° C.                                 500 mPa·s                                      1.0    __________________________________________________________________________

Comparative Example 4

A xanthan gum precipitate obtained similarly to Example 1 was driedwithout prior liquid removal or disintegration. The dried precipitatewas ground to a fine xanthan gum powder 80 mesh or finer in size. Thisxanthan gum was measured for its viscosity in the manner described inExample 1. The results are given below.

                                      TABLE 2    __________________________________________________________________________          Mesh   Drying                      Drying                            Drying          Size   Time Pressure                            Temp Viscosity                                      (1)/(2)    __________________________________________________________________________    Comp. Ex. 4          --     20 hrs                      40˜100 torr.                            40˜90° C.                                 300 mPa·s                                      0.6    __________________________________________________________________________

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method for producing saline soluble xanthan gumcomprising the steps of:(a) producing precipitated xanthan gum bymixing, with stirring, an aqueous solution of xanthan gum with ahydrophilic organic solvent in which the xanthan gum is insoluble; (b)removing liquid from the precipitated xanthan gum to form a cake havinga liquid content of no more than 50 % by weight; (c) disintegrating thexanthan gum cake into particles having an average particle size of from0.3 to 2 cm in diameter; and (d) drying the xanthan gum at a temperaturenot exceeding 80° C.
 2. The method of claim 1 wherein the liquid isremoved by squeezing the precipitated xanthan gum.
 3. The method ofclaim 1 wherein the organic solvent is selected from the groupconsisting of methanol, ethanol, isopropanol, dioxane, acetone,tetrahydrofuran, and combinations thereof.
 4. The method of claim 1wherein the average particle size diameter is from 0.6 to 1.5 cm.
 5. Themethod of claim 1 wherein the liquid content of the cake is from 40 to50% by weight.
 6. The method of claim 1 wherein the xanthan gumparticles are dried at a temperature from 40 to 65° C. and a pressure offrom 40 to 100 Torr.
 7. The method of claim 1 wherein the xanthan gumproduced exhibits a viscosity of not less than 650 mPa as determined ona 0.5 % by weight solution thereof in a 12 % by weight aqueous sodiumchloride solution at 20° C. at 30 rpm using a Brookfield BL viscometerand exhibits a ratio of this viscosity to that determined on a 0.5% byweight solution thereof in distilled water of not less than 1.3.
 8. Themethod of claim 1 wherein the liquid removal is carried out in a V-typedisk press.
 9. The method of claim 1 wherein the liquid removal iscarried out in a V-type disk press having opposing disk shape screensfor pressing the precipitated xanthan gum therebetween.
 10. The methodof claim 9 wherein the screens have openings of not greater than 1 mm².11. The method of claim 9 wherein the screens have a diameter of from0.5 to 1.5 meters and are rotated at a speed of from 1 to 12 rpm. 12.The method of claim 1 wherein the mixing is carried out with a rotatingstirrer and by repeated cycles of rotation of the stirrer, first in onedirection and then in the reverse direction.
 13. The method of claim 12wherein the cycle of rotation comprises rotating the stirrer betweenabout 90 to 360 degrees in one direction and then rotating the stirrerin an equal amount in the reverse direction.
 14. The method of claim 1wherein the dried xanthan gum is ground to a mesh size of 80 mesh orfiner.
 15. The method of claim 1 wherein the liquid is removed bysqueezing the precipitated xanthan gum in a V-type disk press.
 16. Themethod of claim 1 wherein the disintegrated xanthan gum is dried in afluidized air dryer.
 17. The method of claim 1 wherein the mixing iscarried out in a cylindrical tank having an agitator shaft thereinprovided with upper and lower opposing pairs of agitating bladesextending from the agitator shaft and wherein the diameter of the tankto the diameter of a circle defined by the extended blades is at least0.5.
 18. The method of claim 1 wherein the xanthan gum cake isdisintegrated using a disintegrator comprising a treating tank formedfrom a cylindrical wall, a portion of said wall being a screen, a rotarycutter disposed essentially in said cylindrical tank for chopping upxanthan gum which has been introduced to the cylindrical tank, thedisintegrated xanthan gum being discharged from the cylinder through thescreened wall portion.
 19. The method of claim 1 wherein theprecipitated xanthan gum is dried in a dryer comprising a rotatabledrying gum rotatable on a driven rotating shaft, the drum having aninlet and an outlet, and having an outer jacket for receiving hot liquidto heat the interior of the drum.